Direct fermentation for Isobutene, Butadiene and Propylene production: a highway to renewable plastics, synthetic rubber and fuels

Romain CHAYOT

Global Bioenergies, Evry, France

Romain.Chayot@global-bioenergies.com
As of today, most industrial bioproduction processes are based on naturally existing metabolic pathways, limiting the scope of industrial biology, and preventing the access to many of the chemistryâ??s largest markets. The purpose of Global Bioenergies, is to develop innovative metabolic pathways for the production of light olefins from renewable resources, by direct fermentation.
Light olefins (ethylene, propylene, linear butylene, isobutylene and butadiene) are the core of the petrochemical industry, and each one represent a multi-billion dollars market. These markets have been shaped by the historical co-production of light olefins from fossil oil in steam crackers. The recent use of large quantities of shale gas in steam crackers, resulting mostly in the production of ethylene, has changed the market landscape, emphasizing the need for alternative production routes for the other olefins. However, light olefins are not naturally produced by microorganisms and no bioprocess to convert renewable resources to these molecules has been industrialized so far.
Global Bioenergies has developed an artificial metabolic pathway including all the necessary enzymatic reactions from feedstock to isobutene. In contrast with most former approaches, the metabolic route leading to isobutene includes non-naturally occurring reactions as key steps, for example the decarboxylation of hydroxyisovaleric acid into isobutene. Since all these reactions are enzymatic, isobutene can be obtained by direct fermentation, e.g. a process wherein all the chemical transformations are carried on by the host microorganism.
The scale-up of this process is in progress. Importantly, production of a volatile compound such as isobutene (and other light olefins) by direct fermentation presents two major advantages: first, in contrast with what would happen with ethanol or isobutanol for example, the product is spontaneously removed from the culture broth, which alleviates the limitations linked with titer issues. Second, the purification process is considerably easier and cheaper since no energy consuming methods such as distillation or phase separation are necessary to purify the end product.
Scale-up will be carried out in two industrial pilots. A first pilot installed in Pomacle-Bazancourt in France with an annual capacity of 10 tons of oxidation-grade isobutene will target applications such as methacrylic acid (a paint additive) and organic glass. The second pilot, installed on the refinery site of Leuna, Germany, will have an annual capacity of 100 tons of polymer-grade isobutene compatible with the rest of isobuteneâ??s wide product tree including fuels and rubber applications.
Finally, while the isobutene process is progressing towards industrial scale, Global Bioenergies is also developing new artificial metabolic pathways enabling direct bio-production of Butadiene and Propylene.